Assessment and management of patients developing low energy vertebral compression fractures following basivertebral nerve ablation

The ablation of the basivertebral nerve (BNV) is a recent but ostensibly effective treatment for vertebrogenic low back pain. The safety and efficacy of basivertebral nerve ablation is based on several prospective randomized trials that excluded patients with other spinal diagnoses such as scoliosis, spondylolisthesis, and osteoporosis. As BVN ablation has expanded to patients outside of randomized control trials, there has been inclusion of more patients with diagnoses such as scoliosis, spondylolisthesis, and osteopenia or osteoporosis (Figure 1). Elderly patients who are candidates for BNV ablation have a higher incidence of osteoporosis and other degenerative conditions than the patient who were included in the initial prospective randomized trials for ablation of the basivertebral nerve.1–5 In elderly patients with lumbar scoliosis, prominent degenerative disc disease and decreased bone mineral density an increased incidence of low energy vertebral compression fractures (VCFs) has been identified as a new source of back pain following the basivertebral nerve ablation.1 Anteroposterior (A) and lateral (B) conventional radiographs of the lumbar spine taken in an 87-year-old osteoporotic patient with 25 degrees of lumbar levoscoliosis (white lines in panel A), spondylolisthesis (white arrow in panel B), bone density of −2.0, and loss of sagittal balance and lumbar lordosis (white dashed line in panel B) suffered a low energy L2 vertebral compression fracture 40 days following a basivertebral nerve ablation and subsequently underwent an L2 vertebroplasty (white arrowhead in panels A and B). Seventy-four consecutive patients with degenerative disc disease and vertebrogenic back pain from two clinical sites underwent multi-level (2–5 levels) basivertebral nerve ablations over a 1 year time period. There were 8 patients with a new low energy VCFs at an incident vertebral level and one patient who developed sacral insufficiency fractures at a non-incident level. The average age in this fracture group was older at 78 and the fractures occurred at interval average of 69 days following the ablation procedure. The bone density T-score in this group averaged −3.0. Four fractures were at L2, and 1 fracture was at L5. Of the other 4 fractures, 2 were at levels adjacent to prior fusion surgery (Figure 2), 1 was at a level adjacent to a prior kyphoplasty, and the remaining level was at an untreated sacral S2 level in a patient with severe osteoporosis. Of the 9 patients with vertebral fractures, 7 were treated with vertebroplasty and 2 were treated with kyphoplasty. Sagittal T1-weighted (A) and STIR (B) MR images show rounded signal changes at the terminus of the basivertebral nerve (larger white arrows in panels A and B) representing prior basivertebral nerve ablation. The edema present in the L2 vertebral body (white arrowheads in panels A and B) demonstrate the vertebral compression fracture that presented 35 days following the basivertebral nerve ablation. Also noted is the presence of prior anterior lumbar interbody fusion hardware and interbody grafts from L3–4 to L5–S1 (smaller white arrows in panels A and B). Vertebral compression fractures are common and can be seen in almost 20% of the individuals that are 70 years of age or older and can reach double that percentage by age 80. It is almost certain that the osteoporosis and the high risk of vertebral fracture that accompanies advanced age are contributors to the vertebral fractures seen in our population of patients presenting with VCFs after BVN ablation.6 The patients suffering from VCFs after BVN ablation were older with a mean age of 78 years and all had osteoporosis with a mean T-score of −3.0. The incidence of fracture in these patients was much higher at 12% than was seen in the clinical trials (0.4% prevalence of VCFs). The presence of complex spine issues, the advanced age of the patients and the existing osteoporosis are all likely contributors to this higher prevalence of VCFs. The presence of significant osteoporosis subjects the patient to increased risk of VCF and the more advanced the age of the individual treated the less optimal their bone quality.7 The patient with sacral insufficiency fractures, for example, was diagnosed following lumbar basivertebral nerve ablation procedure but the fractures appear to be related to the patients’ severe osteoporosis rather than the prior osseous ablation procedure. The osseous access tools used in the Intracept procedure create little damage to the trabecular bone structure. The radiofrequency ablation (RFA) area is approximately 20% of the vertebral body.1 The radiofrequency energy heats the trabecular bone and likely causes transient weakening of the bone prior to subsequent healing. Previous histopathological analyses on the effect of RFA on bone shows that bone affected by radiofrequency energy is replaced by normal bone and that the new bone is like the remainder of the osseous tissue in regard to its architecture, connectivity and bone mineral content.8 This re-establishment of the normal bone is time dependent and progressively mineralizes over the first 4 weeks following RFA.8 The progressive mineralization was seen to re-establish the normal structure and function in animal models within the first month after treatment, but this histologic analysis was conducted in small animal models where the time to full healing was likely accelerated as compared to humans. An analysis of the major complications associated with RFA of bone tumors showed that secondary fractures were noted at an average of 127.5 days ± 115.8 with a range of 60–300 days.9 As the newly formed bone replaces the bone damaged by the RFA heat there is a point where the underlying bone strength is compromised. The radiofrequency energy used has an effect on the underlying bone and may transiently increase propensity for VCFs. This was seen in patients with a mean age of 63 after undergoing RFA for spine tumors where VCFs occurred at nearly 128 days post RFA. This is compared to our older patients who suffered vertebral fractures an average of 69 days following their BVN ablation procedure.10 These findings suggest that BVN ablation may have a transient negative impact on bone strength that predisposes a high risk osteoporotic patient to a VCF on the average 69 days after their ablation done for vertebrogenic back pain. It should be noted that this is very likely a transient finding as previous Phase I studies have shown that intraosseous BVN ablation does not have a long term adverse effect on the vertebral body as it returns to its pre-treatment strength after a period of normal healing.10 In summary, we have described what appears to be an independent risk factor for developing VCFs in already osteoporotic patients undergoing BVN ablation. The RFA appears to transiently weaken the bone in patients with existing osteoporosis with VCFs appearing on the average approximately two months following the ablation of the basivertebral nerve. Given the utility of BVN ablation and the lack of other acceptable treatment options in this patient population our recommendations are to continue with the current treatment strategy but with the understanding that the patient is at increased risk of developing a VCF. None declared. J.A.H. declares the following disclosures: unrelated to this study I received compensation from Relievant related to consultancy, research and teaching. D.P.B. declares the following disclosures: unrelated to this study I received compensation from Relievant related to consultancy, research and teaching. G.F., J.M., T.R.P., M.S., and S.Y. have no conflicts.